We have demonstrated that carcinogenic N-alkyl-N-nitroso compounds and other DNA damaging agents cause an acute alteration of cellular NAD metabolism. Our studies of the mechanism of this alteration have provided direct evidence that DNA damaging agents cause the rapid conversion of NAD to the chromosomal biopolymer poly(ADP-ribose). Our studies also provide direct evidence that DNA strand breaks are the common factor of DNA damage that greatly stimulates poly(ADP-ribose) synthesis. The proposed studies will utilize sensitive and selective chemical methods developed in our laboratory to study in detail the biosynthesis of poly(ADP-ribose) in vivo in normal cells prior to and following induction of NDA damage. The total levels of poly(ADP-ribose), the rate of turnover, the size distribution of polymer chains and the relationship of a branched structure of poly(ADP-ribose) to the above will be studied. The relationship of mono(ADP-ribose) metabolism in vivo to DNA damage and to poly(ADP-ribose) metabolism will also be studied by application of a newly developed method for measuring mono(ADP-ribose). The relationship of (ADP-ribose) metabolism to possible biological functions related to DNA repair will also be studied. The direct involvement of poly(ADP-ribose) in DNA repair will be studied by examining the effect of specific inhibitors of poly(ADP-ribose) synthesis and/or NAD depletion of cells on the rates of unscheduled DNA synthesis in the absence of hydroxyurea which alters poly(ADP-ribose) metabolism. We will also assess the role of ADP-ribose metabolism in the kinetics of removal of DNA lesions from specific regions of chromatin and study the kinetics of appearance and removal of DNA strand breaks during repair. We will evaluate the possible relationship of ADP-ribose metabolism to the modulation of endonuclease activity and to the modulation of DNA replication following the occurrence of DNA damage. The involvement of a vitamin derived molecule in DNA repair and possibly in other processes involving DNA strand breaks has great potential significance with regard to both the initiation and promotion phases of carcinogenesis.